We propose to assess the predominant site of maximal expiratory flow limitation in the chronic remittent and intermittently acute forms of airways obstruction in patients and to examine the predominant location of acute changes with both bronchoconstrictor and bronchodilator administration in normal subjects. Localization of obstruction and responses will be based upon the degree of density dependence of maximal expiratory flow rates in patients and in normals and by examination of isovolume pressure flow curves in normal subjects. In normal subjects the goal is to more completely examine hypotheses concerning site specificity of bronchodilator action and bronchial constriction. The long term goal in patients is to provide useful information in the classification, prognosis and responses to acute and prolonged therapy of obstructive airways syndromes.